We are going to learn how to create bbs of a column in this article, this is in continuation to our previous article where we learned how to create bbs of a footing.
As you can see from the drawing above there are two kinds of bars in this column. One is long L shaped main bars, and the other are ties that keep the main bars together, in beam we have stirrups but in column we don’t call them stirrup we call them column ties.
So lets start with the Main bars
Length of rebar
Column has a height of 2.4m
Footing has a height of 0.5m
Total height = height of column + height of footing = 2.4+0.5=2.9m
Now as we can see the Main column bars do not go all the way to the bottom of the footing
At the bottom there is a cover of 50mm on top of that we have main bottom bar of 10mm on top of that we have bottom distribution bar of 10mm and on top of that our main column bar sits
Main column bar is 50mm+10mm+10mm=70mm above the bottom of fitting
Height of column bar = 2.9m – 0.07m= 2.83m
There is also L bend in our main column bar of length 25* diameter of bar=25*10 (diameter = 10mm)
Total Length = Height of column + L bend = 2.83+ 0.25 = 3.08m
Deduction
As we already have learned in the basic of bar bending schedule that for every 45 degree bend we apply a deduction equal to d( 1 times diameter)
Here we have one 90 degree bend so we must apply a deduction of 2d to the total length of the bar
Deduction = 2*10=20mm = 0.02m
Effective Length = Total Length – Deduction
= 3.08 – 0.02
= 3.06
Number of bars
In this case we can see that number of bars are 4
In other much complicated cases we use the formulae
No of bars = Distance/spacing + 1
But we won’t do this here because we can simply count the number of bars here.
Unit Weight
We know that Unit weight of any bar = d2/162
Here out diameter= 10mm
Unit weicht = 10*10/162 = 0.617
Total Weight
Total weight. = Length*number*Unit Weight
= 3.06 * 4* 0.617
= 7.55 Kg
Column Ties
Length
As we can see form the image column has a width of 0.25m
But there is a cover of 25mm on both sides
Total Cover = 25mm+25mm=50mm= 0.05m
Effective width= 0.25-0.05=0.2m
Similarly Effective length = 0.2m
Our column has four sides and 2 hooks
Hooks have a length of 5 times diameter = 5*8 (8mm diameter of column ties)
=40mm
2 Hooks = 2*40mm = 80mm
= 0.08m
Length of column = Length of 4 sides + Length of 2 hooks
= 4*0.2 + 0.08
=0.88m
Deduction
As we know for every 45 degree bend we apply a deduction equal to d(diameter of bar)
Here we have hook of 135 degree = 3*45 degree
So we will apply deduction = 3*d
Because we have 2 hooks So total Deduction = 3d+3d=6d
= 6*8 (8mm diameter of ties)
= 48mm
= 0.048m
Effective Length = Length – deduction
= 0.88 – 0.048
= 0.832m
Number of bars
We know that the formulae to calculate the number of bar
Number of bars = Distance/ spacing +1
Ties are placed on the entire length of the bar
So distance is equal to hight of column main bar = 2.83m= 2830
Spacing is given in the drawing equal to 12mm centre to centre
No of bars = 283/12 +1
= 24 + 1 = 25
Unit weight
Unit weight of any rebar = d2/162
= 8*8/162
= 0.395
Total Weight
Total weight =Length*number*Unit Weight
= 0.832 * 25* 0.395
= 8.216 Kg
So here is the full bbs of column
In the next article we are going to learn how to make bar bending schedule of a beam
If you want a free software to make bar bending schedule I highly recommend you download the official BBS app
BBS App Android Google Play Link: Click here to download
iPhone AppStore Line: Click here to download
If you are a fresher civil engineer and want to know how to get a job read this article: How to get a job as a fresher civil engineer.